Optimizing pitch allocation in a cochlear stimulation system

ABSTRACT

Optimizing pitch allocation in a cochlear stimulation system may include implanting an electrode array having a plurality of electrodes into the cochlea of a patient, where the electrode array has an associated implant fitting characteristic that defines a relationship between the implanted electrode array and audio frequencies, presenting sounds through the electrode array to the patient, receiving from the patient a selection of one of the sounds that most closely conforms to a single note, and determining a slope of the implant fitting characteristic of the electrode array based on the sound selected by the patient. Each sound may include a fundamental frequency and one or more harmonics. The optimization may also include changing a center frequency of a band pass filter associated with each electrode based on the determined slope.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/262,055,filed Oct. 28, 2005, now U.S. Pat. No. 8,027,733, to which priority isclaimed and which is incorporated herein by reference in its entirety.

BACKGROUND

The following disclosure relates to cochlear stimulation systems for thetreatment of hearing loss and, more particularly, to a method foroptimizing pitch allocation using a harmonics-based tuner for aligningthe band pass filters associated with an electrode as implemented in acochlear stimulation system.

Generally, there are two types of hearing loss: conductive andsensorineural. Conductive hearing loss occurs when the normal mechanicalpathways for sound to reach the hair cells in the cochlea are impeded,for example, by damage to the ossicles. Conductive hearing losstypically may be treated with the use of a hearing aid system, whichamplifies sound so that acoustic information can reach the cochlea andthe hair cells, or through surgical procedures. Hearing aids, however,are not effective for treating sensorineural hearing loss, no matter howloud the acoustic information is amplified, given the hair cells in thecochlea are either absent or destroyed.

Sensorineural hearing loss occurs when the hair cells in the cochlea,which are needed to transduce acoustic signals into auditory nerveimpulses, are either absent or destroyed. Sensorineural hearing losstypically may be treated with a cochlear stimulation system, such as thesystems described in U.S. Pat. Nos. 5,938,691 and 6,219,580, each ofwhich is incorporated herein by reference. These cochlear stimulationsystems produce sensations of sound in patients with sensorineuralhearing loss by direct electrical stimulation of the ganglia of theauditory nerve cells. These systems bypass the defective cochlea haircells that normally transduce acoustic energy into electrical activityin such nerve cells, leading to perception of sound in the patient'sbrain.

Cochlear stimulation systems typically include an electrode array, animplantable cochlear stimulator (“ICS”), an externally wearable signalprocessor (or speech processor, portions of which can be implanted) anda microphone. The speech processor generally employs a headpiece thatholds the microphone to be positioned adjacent to the patient's ear. Inoperation, the electrical stimulation applied to the ganglia is derivedfrom acoustic signals received by the microphone and transformed intocontrol data by the speech processor that is programmed during a fittingprocess to meet the particular requirements of each patient. The speechprocessor transmits the control data to the ICS, which uses the controldata to selectively generate electrical stimuli and to apply theelectrical stimuli to one or more cochlea stimulating channels, eachassociated with an individual electrode or a pair or group of electrodeswithin or on the electrode array, which is typically surgically insertedinto the patient's cochlea.

Within the cochlea, there are two main cues that convey “pitch”(frequency) information to the patient. They are (1) the place orlocation of stimulation along the length of a cochlear duct and (2) thetemporal structure of the stimulating waveform. Because each place alongthe cochlea corresponds to a specific perceived sound frequency, therelationship between the cochlear place and perceived sound frequency istypically different for every individual as no two cochleas are alikeand the nerve wiring between the cochlea and to the brain is differentfor every individual. In the cochlea, received sound frequencies aremapped to a “place” in the cochlea, generally from high to low soundfrequencies from the basilar to apical direction.

At present, many patients fitted with a cochlear stimulation system findit difficult to enjoy music generally because the mapping of theelectrode array in a cochlear duct to the perceived audio frequencies isnot correct. Correctly mapping an electrode array in a cochlear duct tothe perceived audio frequencies is complicated by differences in apatient's anatomy as mentioned above. Often times, when the electrodearray is surgically inserted into a patient's cochlea, the finalimplanted position of the electrode array is misaligned with the properplace along the patient's cochlea. Moreover, the nuances of the electricfield propagation at each electrode contact in the electrode array tendsto be variable. Both the misalignment of the electrode contacts andvariability of the electric field propagation leads to an arbitrarinessto a mapping scheme between the electrode contact and the perceivedsound frequency—i.e., the perceived sound frequencies are not the sameas the correct received sound frequencies. Conventional fitting programsthat process delivery of certain received sound frequencies through aselected electrode contract or electrode contacts typically do notcompensate for this misalignment and variableness.

U.S. Pat. No. 7,702,396, incorporated herein by reference, attempts toovercome these problems by providing an improved fitting tool to betterconvey pitch information to a user of a cochlear implant. The disclosedmethods and systems provide a fitting routine using melodies to helpproperly map specific electrodes and/or “places” on the cochlear tocorresponding perceived audio frequencies. The use of melodies, however,for tuning or mapping tends to be problematic for those users havingpoor auditory memory or musical training.

SUMMARY

The present inventors recognized that that an improved fitting tool wasneeded, particularly for those patients with poor auditory memory, tocorrectly and more easily map or tune misaligned electrode contacts tothe perceived sound frequencies. The present inventors also recognizedthat the precise position of each electrode contact of the implantedelectrode array could be adjusted or aligned by changing the centerfrequency of a BPF associated with each electrode, but that thedetermination of which center frequency to start at and the necessarychange to the center frequency typically is not easy and is typicallyestimated at the outset for each patient, which also tends to beinaccurate for that patient. Consequently, the present inventorsdeveloped systems and techniques that utilize a harmonics-based tunerfor adjusting the center frequencies of the BPF(s) associated with eachimplanted electrode contact to easily and correctly map each implantedelectrode contact to the perceived audio frequencies. In general, thepatient is allowed to listen to various predetermined harmonic-basedsounds, all but one will sound like a chord, while one will sound like asingle note. The patient's task is to pick the sound that sounds like asingle note. The implant fitting line and slope (mm/octave) thatcorresponds to the single note sound describes the actual position ofthe implanted electrode array. The center frequencies of the BPF(s)associated with each implanted electrode contact are then adjusted basedon the determined implant fitting slope.

Implementations of the system and techniques described here may includevarious combinations of the following features.

A technique to fit a cochlear implant system may include implanting anelectrode array having a plurality of electrodes into the cochlea of auser, where the electrode array has an associated implant fittingcharacteristic that defines a relationship between the implantedelectrode array and audio frequencies, presenting sounds to the userthrough the electrode array, wherein each sound includes a fundamentalfrequency and harmonics, receiving from the user a selection of one ofthe sounds that most closely conforms to a single note, and determininga slope of the implant fitting characteristic of the electrode arraybased on the sound selected by the user. The technique may also includechanging a center frequency of a band pass filter associated with eachelectrode based on the determined slope. The step of presenting thesounds to the user through the electrode array may include presentingrepetitively the sounds to the user by pressing keys of a keyboard orkeypad, where each key is associated with one of the sounds.

A technique to tune a filter associated with an intra-cochlear electrodemay include defining a plurality of audio presentations (where eachaudio presentation includes a fundamental frequency and harmonics),presenting the defined audio presentations to a patient, receiving fromthe patient a selection of an audio presentation that most closelysounds like a single note, and adjusting a center frequency of thefilter based on the selected audio presentation. The step of presentingthe defined audio presentations to the patient may be initiated bypressing keys of a keyboard or keypad, each key being associated withone of the defined audio presentations. The step of adjusting the centerfrequency of the filter based on the selected audio presentation mayinclude determining a slope of the intra-cochlear electrode based on theselected audio presentation.

A cochlear implant fitting system may include an implantable cochlearstimulator, an electrode array having a multiplicity of electrodesconnected to the implantable cochlear stimulator, and a means forgenerating a sound including a fundamental frequency and a plurality ofharmonics delivered through the electrode array. The cochlear implantsystem may also include a means for adjusting a slope of an implantfitting line embodied in presenting the sound, and a means for adjustingan offset of the implant fitting line.

The systems and techniques described here may provide one or more of thefollowing advantages. The techniques may be performed quickly and easilyin a clinical setting and yield an accurate result of the implantfitting line and slope of an inserted electrode array. Moreover, the useof the harmonics-based tuner may be utilized with fitting software toallow easier and better tuning of the processing software for a patient.Hence, the use of currently available fitting systems, such asSOUNDWAVE™ from ADVANCED BIONICS® Corporation, to allow the dynamicmanipulation of the BPFs during the filter alignment process may bepossible.

Details of one or more implementations are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a typical cochlear stimulation system in which theharmonic-based tuner and techniques may be implemented.

FIG. 2 depicts a partial functional block diagram of a cochlearstimulation system, in which the harmonic-based tuner and techniques maybe implemented;

FIG. 3 illustrates the intrinsic line of an individual's cochlea and animplant fitting line, or characteristic, showing both lateral andabsolute misalignment.

FIG. 4 represents the linear relationship of musical notes to placesalong an individual's cochlea.

FIGS. 5A and 5B illustrates the harmonic relationship between notesplayed on one instrument (a flute in FIG. 5A) and the same notes playedon another instrument (a violin in FIG. 5B).

FIG. 6 depicts in flow chart form an implant fitting routine utilizing aharmonics-based tuner and technique for aligning the band pass filtersassociated with each implanted electrode contact so as to permit thecorrect mapping of the implanted electrode array to the perceived audiofrequencies.

FIG. 7 depicts an example of a menu interface to a computer softwareprogram that may be used to implement the steps described in FIG. 6.

FIGS. 8A and 8B depict in flow chart form an alternative implementationof the fitting routing utilizing a harmonics-based tuner for aligningthe band pass filters associated with each implanted electrode contactso as to permit the correct mapping of the implanted electrode array tothe perceived audio frequencies.

FIGS. 9A-9C illustrate in graphical form the alternative implementationof the fitting routine described in FIGS. 8A and 8B.

FIGS. 10A and 10B show an example of a menu interface to a computersoftware program that can be used to implement the steps presented inFIGS. 8A and 8B.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The following disclosure describes a tool to better determine theimplant fitting line, or characteristic, and slope for a cochlearstimulation system. A harmonics-based tuning method may be used toproperly map specific electrodes and/or “places” on the cochlea tocorresponding perceived audio frequencies. This mapping may be referredto as an “implant fitting line” (or implant fitting characteristic) anddepends in particular on the type of electrode array used, the type ofcochlear stimulation system, and the patient's anatomical variation.From the implant fitting line, the slope (mm/octave) may be determined.When the implant fitting line is properly determined and implemented ina cochlear stimulation system, the patient typically is able toexperience a significant improvement in the perceived quality of sound,particularly with music and speech.

FIG. 1 depicts one implementation of a cochlear stimulation system inwhich the harmonic-based tuning method may be implemented. The systemincludes a speech processor portion 10 and a cochlear stimulationportion 12. The speech processor portion 10 includes a speech processor(SP) 16 and a microphone 18. The microphone 18 may be connected directlyto the SP 16 or may be coupled to the SP 16 through an appropriatecommunication link 24. The cochlear stimulation portion 12 includes animplantable cochlear stimulator (ICS) 21 and an electrode array 48. Theelectrode array 48 is typically adapted to be inserted within a duct ofthe cochlea. The array 48 includes a multiplicity of electrodes 50,e.g., sixteen electrodes spaced along its length that are selectivelyconnected to the ICS 21. The electrode array 48 may be substantially asshown and described in U.S. Pat. No. 4,819,647 or U.S. Pat. No.6,129,753, incorporated herein by reference. Electronic circuitry withinthe ICS 21 allows a specified stimulation current to be applied toselected pairs or groups of the individual electrodes included withinthe electrode array 48 in accordance with a specified stimulationpattern, defined by the SP 16.

The ICS 21 and the SP 16 are shown as linked together electronicallythrough a suitable data or communications link 14. In some cochlearstimulation systems, the SP 16 and microphone 18 comprise the externalportion of the cochlear stimulation system and the ICS 21 and electrodearray 48 comprise the implantable portion of the system. Thus, the datalink 14 may be a transcutaneous (through the skin) data link that allowspower and control signals to be sent from the SP16 to the ICS 21. Insome implementations, data and status signals may also be sent from theICS 21 to the SP 16.

Typically, where a transcutaneous data link must be established betweenthe external portion and the implantable portions of the system, suchlink is realized by an internal antenna coil within the implantableportion and an external antenna coil within the external portion. Inuse, the external antenna coil is aligned over the location where theinternal antenna coil is implanted, allowing such coils to beinductively coupled to each other, thereby allowing data, e.g., themagnitude and polarity of a sensed acoustic signals and power to betransmitted from the external portion to the implantable portion. Note,in other implementations, both the SP 16 and the ICS 21 may be implantedwithin the patient, either in the same housing or in separate housings.If in the same housing, the link 14 may be realized with a direct wireconnection within such housing. If in separate housings, as taught,e.g., in U.S. Pat. No. 6,067,474, incorporated herein by reference, thelink 14 may be an inductive link using a coil or a wire loop coupled tothe respective parts.

The microphone 18 senses acoustic signals and converts such sensedsignals to corresponding electrical signals and may thus be consideredan acoustic transducer. The electrical signals are sent to the SP 16over a suitable electrical or other link 24. The SP 16 processes theseconverted acoustic signals in accordance with a selected speechprocessing strategy to generate appropriate control signals forcontrolling the ICS 21. Such control signals specify or define thepolarity, magnitude, location (which electrode pair or electrode groupreceive the stimulation current), and timing (when the stimulationcurrent is applied to the electrode pair) of the stimulation currentthat is generated by the ICS. Such control signals thus combine toproduce a desired spatio-temporal pattern of electrical stimuli inaccordance with the desired speech processing strategy. Unlike earliercochlear stimulation systems, more recent cochlear stimulation systemsconfine such control signals to circuitry within the implantable portionof the system, thereby avoiding the need to continually send or transmitsuch control signals across a transcutaneous link.

The speech processing strategy is used, among other reasons, tocondition the magnitude and polarity of the stimulation current appliedto the implanted electrodes 50 of the electrode array 48. Such speechprocessing strategy involves defining a pattern of stimulation waveformsthat are to be applied to the electrodes as controlled electricalcurrents.

Analog waveforms used in analog stimulation patterns are typicallyreconstructed by the generation of continuous, short monophasic pulses(samples). The sampling rate is selected to be fast enough to allow forproper reconstruction of the temporal details of the signal. An exampleof such a sampled analog stimulation pattern is a simultaneous analogsampler (SAS) strategy.

FIG. 2 shows a partial functional block diagram of the SP 16 and the ICS21 of an exemplary cochlear stimulation system in which theharmonic-based tuner may be implemented. A complete description of thefunctional block diagram of this cochlear stimulation system may befound in U.S. Pat. No. 6,219,580 ('580 patent), which is incorporatedherein by reference. In the manner described in the '580 patent, thecochlear stimulation system functionally shown provides n analysischannels that may be mapped to one or more stimulus channels. That is,after the incoming sound signal is received through the microphone 18and the analog front end circuitry (AFE) 22, it is digitized in ananalog to digital (A/D) converter 28 and then subjected to appropriategain control (which may include compression) in an automatic gaincontrol (AGC) unit 29. After appropriate gain control, the signal isdivided into n analysis channels, each of which includes a band passfilter, BPFn 30, centered at a selected frequency. The signal present ineach analysis channel is processed as described more fully in the '580patent or as is appropriate using other signal processing techniques andthe signals from each analysis channel are then mapped, using mappingfunction 41, so that an appropriate stimulus current of a desiredamplitude and timing, may be applied through a selected stimulus channelto an electrode contact to stimulate the auditory nerve. Thus, theinformation contained in the n “analysis channels” is appropriatelyprocessed, compressed and mapped in order to control the actual stimuluspatterns that are applied to the patient by the ICS 21 and itsassociated electrode array 48.

The electrode array 48 includes a multiplicity of electrode contacts 50,connected through appropriate conductors to respective currentgenerators or pulse generators within the ICS. Through thesemultiplicity of electrode contacts, a multiplicity of stimulus channels,e.g., m stimulus channels, exist through which individual electricalstimuli may be applied at m different stimulation locations or placeswithin the patient's cochlea or other tissue stimulation site.

While it is common to use a one-to-one mapping scheme between theanalysis channels and the stimulus channels, wherein n=m, and the signalanalyzed in the first analysis channel is mapped to produce astimulation current at the first stimulation channel, and so on, it isnot necessary to do so. Instead, in some instances, a different mappingscheme may prove beneficial to the patient. For example, assume that nis not equal to m (n, for example, could be at least 20 or as high as32, while m may be no greater than sixteen, e.g., 8 to 16). The signalresulting from analysis in the first analysis channel may be mapped,using appropriate mapping circuitry 41 or equivalent, to the firststimulation channel via a first map link, resulting in a firststimulation site (or first area of neural excitation). Similarly, thesignal resulting from analysis in the second analysis channel of the SP16 may be mapped to the second stimulation channel via a second maplink, resulting in a second stimulation site. Also, the signal resultingfrom analysis in the second analysis channel may be jointly mapped tothe first and second stimulation channels via a joint map link. Thisjoint link results in a stimulation site that is somewhere in betweenthe first and second stimulation sites.

The “in-between” site at which a stimulus is applied may be referred toas a “stimulation site” produced by a virtual electrode. This capabilityof using different mapping schemes between n analysis channels and mstimulation channels to thereby produce a large number of virtual andother stimulation sites provides flexibility with respect to positioningthe neural excitation areas precisely in the cochlear place that bestconveys the frequencies of the incoming sound. Through appropriateweighting and sharing of currents between two or more physicalelectrodes, it is possible to provide a large number of virtualelectrodes between physical electrodes, thereby effectively steering thelocation at which a stimulus is applied to almost any location along thelength of the electrode array.

The output stage of the ICS 21, which connects with each electrode E1,E2, E3, . . . Em of the electrode array, may be as described in U.S.Pat. No. 6,181,969, which is incorporated herein by reference. Such anoutput stage provides a programmable N-DAC or P-DAC (where DAC standsfor digital-to-analog converter) connected to each electrode so that aprogrammed current may be sourced to the electrode or sunk from theelectrode. Such configuration allows any electrode to be paired with anyother electrode and the amplitudes of the currents may be programmed andcontrolled to gradually shift the stimulating current that flows fromone electrode through the tissue to another adjacent electrode orelectrodes, thereby providing the effect of “shifting” the current fromone or more electrodes to another electrode(s). Through such currentshifting, the stimulus current may be shifted or directed so that itappears to the tissue that the current is coming from or going to analmost infinite number of locations.

The speech processing circuitry 16 generally includes all of thecircuitry from point (C) to point (A). In prior art cochlear stimulationsystems, the entire SP circuitry was housed in a speech processor thatwas part of the external (or non-implanted) portion of the system. Thatis, in such prior art systems, only the ICS 21 and its associatedelectrode array were implanted, as indicated by the bracket labeled“Imp1” (for “Implant-1”). This means that in such prior art systems, thesignal passing through the serial data stream at point (A) is also thesignal that must pass through the transcutaneous communication link fromthe external unit to the implanted unit. Because such signal containsall of the defining control data for the selected speech processingstrategy for all m stimulation channels, it therefore has a fairly highdata rate associated therewith. As a result of such high data rate,either the system operation must be slowed down, which is generally notdesirable, or the bandwidth of the link must be increased, which is alsonot desirable because the operating power increases.

In contrast to prior art systems, a modern cochlear stimulation system,such as the CII Cochlear Stimulation System manufactured by ADVANCEDBIONICS® Corporation of Sylmar, Calif., advantageously puts at least aportion of the speech processor 16 within the implanted portion of thesystem. For example, a cochlear stimulation system may include the PulseTable and arithmetic logic unit (ALU) 43 inside of the implantedportion, as indicated by the bracket labeled “Imp2.” Such partitioningof the speech processor 16 offers the advantage of reducing the datarate that must be passed from the external portion of the system to theimplanted portion. That is, the data stream that must be passed to theimplanted portion Imp2 comprises the signal stream at point (B). Thissignal is essentially the digitized equivalent of the modulation dataassociated with each of the n analysis channels, and (depending upon thenumber of analysis channels and the sampling rate associated with each)may be significantly lower than the data rate associated with the signalthat passes through point (A). Hence, improved performance withoutsacrificing power consumption may be obtained with such a cochlearimplant.

Future generations of cochlear stimulation systems may incorporate moreand more of the speech processor 16 within the implanted portion of thesystem. For example, a fully implanted speech processor 16 wouldincorporate all of the SP in the implanted portion, as indicated by thebracket labeled Imp3. Such a fully implanted speech processor offers theadvantage that the data input into the system, i.e., the data streamthat passes through point (C), would need only have a rate commensuratewith the input acoustic signal.

Additional features made possible by the cochlear stimulation systemshown in FIG. 2 or equivalents, which may be used in conjunction withthe presently described harmonics-based tuner, allow the current stimulito be applied to the target tissue at fast rates and in a way that morenaturally elicits a stochastic firing of the target tissue.

FIG. 3 illustrates the intrinsic line, or characteristic, of anindividual's cochlea and an implant fitting line showing both lateraland absolute misalignment. The line E may be referred to as the“intrinsic line” having an “intrinsic slope” for a patient's cochlea.The intrinsic line E, which is the lower line, represents the actualrelationship between the cochlear place (mm) versus the associated log(frequency of the perceived sound of that place). In an individual'sear, each place along the cochlea corresponds to a specific perceivedsound frequency. This relationship between cochlear place and perceivedsound frequency is typically different for every individual, since notwo cochleas are alike and the nerve wiring between the cochlea and tothe brain is different for every patient. The slope of the intrinsicline E may be calculated, where the slope is the change in cochlearplace over the change in log (frequency of the perceived sound of thatplace).

The implant fitting line D, which is the upper line, represents theimplant fitting line of the cochlear stimulation system. The implantfitting line D, which maps the electrode place versus log (frequency ofthe perceived sound), is typically also different for every patient. Ascan be seen, the implant fitting line is misaligned with the intrinsicline E. To properly perceive sounds, as produced through a particularcochlear stimulation system, including a specific electrode array, thesystem must be “fitted” or “tuned” to accommodate the individualanatomical differences, the particular configuration of the electrodearray, and the electrode.

Assume that a 2000 Hz incoming sound is picked up (or delivered) by thecochlear stimulation system. The patient then should perceive a 2000 Hztone but that is not typically the case. After the electrode array isimplanted, an estimate is typically made for what the correct implantfitting line D (including slope) should be. The slope of the implantfitting line D is the change in electrode distance (corresponding to aparticular electrode place) over the change in log (frequency of theperceived sound at that place). Because of variability in anindividual's anatomical cochlea, invariably the estimated implantfitting line D (and slope) will not initially correspond to theintrinsic line E. The goal is to adjust (tune) the implant fitting lineD to match or overlap the intrinsic line E, or at least to have the sameslope as intrinsic line E, such that a harmonic-relationship between thetwo lines is established, i.e., even if the implant fitting line D doesnot overlap the intrinsic line E, a musical tune typically will berecognized, as each note in relationship to other notes in a tune aregenerally in a harmonic relationship.

As seen in FIG. 3, stimulation must be applied at a slightly differentcochlear place than was originally guessed to yield a perceivedfrequency of 2000 Hz. For example, the electrode and cochlear place tobe stimulated is at about 11 mm for the intrinsic line D, not thepredicted 10 mm for the implant fitting line E. Such pitch warping makesenjoyment of music difficult. However, if the electrode array positionin the cochlea is altered slightly, either placed further into thecochlea or slightly out from the cochlea, the relationship of each“place” along the electrode array would again change in relationship.Thus, to determine the slope of the electrode array “place” along theelectrode array and the corresponding perceived audio frequency, theelectrode array typically must be adjusted during the fitting procedure.

FIG. 4 represents, in a simplified way, the relationship of musicalnotes to cochlear place. A place on the cochlea corresponds to notes ona musical scale, as represented by notes on a piano scale. Music theoryteaches that there are twelve semitones per octave, i.e., there aretwelve notes (e.g., piano keys) between a C note 306 on one octave and aC note 308 on the next higher octave. As can be seen, the line 310formed by the notes over four octaves is nearly linear. As a result,determining the correct implant fitting slope (in mm/octave), whichresults in a fitting line that is parallel to the intrinsic line, willhelp a patient hear and appreciate music.

FIGS. 5A and 5B illustrates the harmonic relationship between notesplayed on one instrument (a flute in FIG. 5A) and the same notes playedon another instrument (a violin in FIG. 5B) is illustrated. Generally,each musical note has a tone having a fundamental frequency F1 andsubsequent harmonics that are multiples of the tone, i.e., a secondharmonic having a frequency 2*F1, a third harmonic having a frequency3*F1, and so on. The harmonics associated with a particular notegenerally have an amplitude substantially smaller than the amplitude ofthe tone of the note. Also, generally the difference between a note onone instrument (e.g., a flute) and the same note on a differentinstrument (e.g., a violin) is the relative amplitude of the harmonics.

For example, in comparing the note G4, having a fundamental frequency of392 Hz, played on a flute (as shown in FIG. 5A) to the same note playedon a violin (as shown in FIG. 5B), the main differences are the relativeamplitudes of the harmonics. In this example, the amplitudes of theharmonics 510 of the note G4 played on the flute are much smaller thanthe amplitudes of the harmonics 512 of the note G4 played on the violin.Even with these differences in harmonics, in both the flute and theviolin, the only note heard is G4. Thus, the harmonics of a particularnote may be used to determine the correct implant fitting slope (inmm/octave) for the band pass filters used for each implanted electrodecontact.

FIG. 6 depicts in flow chart form an implant fitting routine utilizing aharmonics-based tuner and technique for aligning the band pass filtersassociated with each implanted electrode contact so as to permit thecorrect mapping of the implanted electrode array to the perceived audiofrequencies. To correctly map the electrode array to the perceived audiofrequencies, the patient's implant fitting slope typically must bedetermined, which as noted above, generally is a difficult task becausethe implant fitting slope depends on the patient's anatomy, theelectrode array configuration used, and the position of the electrodearray relative to the cochlea. The tuner fitting routine herein utilizesa harmonics-based tuner for determining the implant fitting slope for aparticular patient.

The fitting routine utilizing the harmonics-based tuner may beimplemented in software and include a graphical user interface and inputdevice, such as keyboard or mouse. Generally, the fitting routine allowsa patient fitted with a cochlear stimulation system to select whichsound from a plurality of predetermined sounds, e.g., ten sounds ofpredetermined duration (such as 1 to 2 seconds), is presented bypressing one of the digit keys 0-9 on a keyboard or key pad.

Each keyboard digit key may be associated with a different predeterminedsound. Each predetermined sound may be a different complex of theharmonics of an arbitrary note (e.g., a C note) and is based on adifferent slope (e.g., mm/octave). In this implementation, the complexesincluded the fundamental frequency and four harmonics of the note. Inother implementations more or fewer harmonics may be used to comprisethe complex. One of these complexes generally will sound like a singlenote to a normal (i.e., unassisted) hearing listener (which may bereferred to as the actual target sound), but to a patient fitted with acochlear stimulation system, the sound presentation would generallysound like a chord (e.g., two or more notes in harmonic relationship)due to the electrode array misalignment. Likewise, the other complexeswill generally sound like a chord to a normal hearing listener, but to apatient fitted with a cochlear stimulation system, one of these othercomplexes will generally sound like a single note (which may be referredto as the perceived target sound). The perceived target sound will havea slope that corresponds to the actual implant fitting slope of theelectrode array. The actual implant fitting slope may then be used todetermine how much to adjust the center frequencies of the band passfilters associated with the electrode contacts. This may done usingADVANCED BIONICS® SOUNDWAVE™ fitting software.

To determine the harmonics that make of the various complexes, it isuseful to know the slope effect on center frequencies of a cochlearplace. The frequencies along the cochlea may be approximated by thefollowing equation, which relates the center frequency of one cochlearplace (CF₁) to that of another (CF_(m)), where m is the distance inmillimeters along the cochlea from the location of CF₁, and S is theslope in form of octaves/mm:CF _(m) =CF ₁(2^(mS))  (1)In the default case of the cochlea (i.e., for an unassisted hearinglistener), S may be estimated to be the default value of S=S_(d)=0.25octaves/mm. If the electrode contact deviates from the default, theslope may be described as:S=S _(d)+ε_(s),  (2)where ε_(s) is the deviation in octaves/mm.

The harmonics of a fundamental frequency (f₀) of a note are defined asthe integer multiples of f₀. To form the complex of harmonics of anarbitrary note, the harmonics that are chosen are those defined by thefollowing equation:f _(h) =f ₀(2^(h)),  (3)where h is an integer.

Given the identical form of equations (1) and (3), a harmonic of thefundamental frequency (f₀) of a particular note that corresponds tointeger h along the basilar membrane of the cochlear may be located,i.e., the cochlear place of any harmonic may be found along the basilarmembrane of the cochlea. The cochlear place (m) of any harmoniccorresponding to h, may be found along the basilar membrane of thecochlea according to the following equations:

$\begin{matrix}{{h = {mS}};{m = \frac{h}{S}}} & (4)\end{matrix}$

The harmonics of the arbitrary note may be “remapped” to correspond tothe actual electrode position, and the slope is changed by some valueε_(s) (in octaves/mm). One way of looking at this problem is that theharmonic corresponding to h will shift. If h_(d) is the default harmonicand the “shifted” harmonic is h_(d)′ then,

$\begin{matrix}{h_{d}^{\prime} = {{mS} = {{m\left( {S_{d} + ɛ_{s}} \right)} = {h_{d} + \frac{ɛ_{s}h_{d}}{S_{d}}}}}} & (5)\end{matrix}$The modified frequencies of the harmonics then are:

$\begin{matrix}{f_{h_{d}}^{\prime} = {f_{0}\left( 2^{h_{d} + \frac{ɛ_{s}h_{d}}{S_{d}}} \right)}} & (6)\end{matrix}$Thus, for any change ε_(s) in the slope, a collection of perceivedharmonics of the fundamental frequency (f₀) may be determined. In anormal hearing person (i.e., an unassisted hearing listener), ε_(s) is0, and equation (6) reduces to the relation shown in equation (3).Therefore, equation (6) may be used to create the various differentcomplexes of the predetermined sounds, each of which may be assigned toa particular digit key on a keypad or keyboard.

As an example, a predetermined sound may be represented by the followingcomplex in frequency space:C=w ₀δ(f ₀)+w ₁δ(f ₁)+w ₂δ(f ₂)+w ₃δ(f ₃)+w ₄δ(f ₄),  (7)where w_(i) is the amplitude of a given harmonic i, f_(i) is thefrequency of that harmonic, and δ(f _(i)) is the delta function at thefrequency f_(i).

As stated above, the fundamental frequency (f₀) is used in each complexand corresponds to the default center frequency of the first filter. Inthis example, f₀ is 371 Hz. In the normal complex (i.e., ε_(s)=0 andS_(d)=0.25 octaves/mm) the frequencies comprising the complex (f₀₋₄)computed using equation (6) are 371 Hz, 742 Hz, 1484 Hz, 2968 Hz and5936 Hz, respectively. In a shifted complex (e.g., with ε_(s)=0.083octaves/mm), the frequencies comprising the complex (f₀₋₄) computedusing the equation (6) are 371 Hz, 935 Hz, 2355 Hz, 5934 Hz and 14952Hz, respectively. Other shifted complexes may be created by changingε_(s). In this implementation, ε_(s) may be selected between −0.5octave/mm and 0.5 octave/mm, i.e., −0.5<ε_(s)<0.5.

The keyboard digit key associated with the actual target sound may beconsidered the target key, which may be automatically changed randomlyeach time the implant fitting routine starts. Depending on the tunerfrequency resolution, the harmonics associated with each digit key mayget further apart or closer together going away from the target key.Thus, the patient's task is to press the digit keys in any order, listento the sound generated as a result of pressing a particular digit key,and choose the sound that sounds most like a single note as opposed to achord.

The implant fitting routine starts at block 702 and then proceeds to thefirst operation, represented by box 703, where the audiologist orpatient may select the frequency resolution of the tuner (the step bywhich ε_(s) will change for each key or button), where a larger numbermay indicate a “fine” frequency resolution and a smaller number mayrepresent a “coarse” frequency resolution. The selected resolutioneffects how far apart (“coarse resolution”) or closer together (“fineresolution”) the harmonics are with respect to each predetermined sound.In alternative implementations, the operation represented by box 703need not be implemented. Next as shown in box 704, the audiologist orpatient defines the default value for ε_(s). Here, ε_(s) typically willbe 0. Next as shown in box 705, the audiologist or patent defines aplurality of sounds, e.g., one sound mapped to each digit key of akeypad or keyboard.

As shown in box 708, the patient selects a sound to be presented fromone of the ten predetermined sounds defined in box 705, e.g., bypressing one of the digit keys on a keyboard. Next, as shown in box 710,the selected sound is presented to the patient. As noted above, thepatient is previously fitted with a cochlear stimulation system, whichprocesses the received sound and stimulates the cochlea. Then, as shownin box 712, after the patients listens to the sound, the patientdetermines whether the perceived sound presentation sounds like a singlenote or a chord. When the target key is pressed, e.g., and the patientdetermines that the sound presentation does not sound like a singlenote, then this is an indication that the cochlear stimulation system ismistuned (i.e., the implanted electrode array is misaligned with thecochlear place), as the patient is actually hearing differentfrequencies than those that are actually being delivered to the patient.As mentioned previously, the predetermined sound associated with thetarget key would sound like a single note to a normal hearing listener.

In the event the patient determines the sound presentation does notsound like a single note, but sounds more like two or more notes, theprocess proceeds to box 708, where the patient selects another sound tobe presented, by, e.g., pressing another digit key. This process isiterative until the patient determines the sound presentation soundslike a single note (i.e., the perceived target sound), at which pointthe pitch allocation in the patient's cochlear stimulation system islikely optimized or close to being optimized and the implant fittingslope may then be determined and the band pass filters associated witheach of the electrodes of the electrode array may be adjusted based onthe determined slope, as shown in box 720.

Once the patient determines which sound presentation sounds like asingle note (i.e., the perceived target sound), the implant fittingslope may be determined based on the ε_(s) associated with the soundpresentation that the patient determined sounded like a single note andequation (2), i.e., where the implant fitting slope is equal to(S_(d)+ε_(s)). Here, the implant fitting slope is adjusted uniformlyacross the entire electrode array. Based on this uniform implant fittingslope, each band pass filter may be adjusted or tuned to correctly mapthe implanted electrode array to the perceived audio frequencies. Forexample, the determined implant fitting slope may be provided as inputto a cochlear fitting software, such as SOUNDWAVE™ from ADVANCEDBIONICS® Corporation, which computes the center frequency of each bandpass filter associated with the electrodes on the implanted electrodearray based on the inputted implant fitting slope. In this manner, thefitting routine utilizing a harmonics-based tuner provides a correctmapping so that a sound perceived by the patient fitted with a cochlearstimulation system would sound like the same sound perceived by a normalhearing listener.

The disclosed fitting routine is notable because determination of theimplant fitting slope of the implant fitting line does not requirespecial musical training. A subject can quickly ascertain whether asound presentation sounds like a single note. Not only is the disclosedfitting routine accurate, but the routine can be completed relativelyquickly in a clinical setting because such sound presentations can bequickly implemented with appropriate programmable software. Because thedisclosed fitting routine is based on the subject determining whether asound presentation is a single note or a chord, the disclosed fittingroutine is suited for those subjects that were pre-lingual at the onsetof deafness, as wells those subjects that have had previous auditoryexperience.

FIG. 7 depicts an example of a menu interface to a computer softwareprogram that may be used to implement the steps described in FIG. 6. Themenu interface at section 806 provides directions to the patient on howto use the computer software program. As can be seen, the patient isnotified that one of the number keys 0 to 9 presents a sound comprisedof one note and the remaining number keys present sounds containing twonotes played at the same time. The patient is directed to press the“RETURN” key after each number key selection. If the patient believes asound presentation consists of a single note, the patient is directed topress the letter key “q”.

At section 810, a log of the patient's actions may be displayed. Here,the patient initially selected the number key “1” and then pressedreturn (as noted by label 814). The predetermined sound associated withthe number key “1” was then presented to the patient. The patient thenselected the number key “4” and then pressed return (as noted by label816). Again, the predetermined sound associated with the number key “4”was then presented to the patient. The patient repeated this process ofselecting a number key, pressing return and listening to soundassociated with the selected number key until the patient eventuallypressed the letter “q” (as noted by label 818) after having listened tothe sound associated with the number key “2”. To the patient, theperceived target sound, which was associated with the number key “2,”sounded like a single note (as shown by label 824) with a actual (ordelivered frequency) of 346.67 Hz (as shown by label 830). In this case,the target key was arbitrarily chosen to be the number key “7” (as shownby label 820) with an actual target frequency of 381.46 Hz (as shown bylabel 826).

The algorithms described above were then used to calculate the estimatedoffset 838 and the implant line slope 834. As can be seen, the offset838 was calculated to be −1.66 semitones and the implant line slope 834was calculated to be 7.51 mm/octave. Based on this information, the bandpass filters associated with each electrode on the electrode array maythen be adjusted resulting in a correct mapping of the electrodes to theperceived audio frequencies.

FIGS. 8A and 8B depict in flow chart form an alternative implementationof the fitting routing utilizing a harmonics-based tuner for aligningthe band pass filters associated with each implanted electrode contactso as to permit the correct mapping of the implanted electrode array tothe perceived audio frequencies. As noted above, to correctly map theimplanted electrode array to the perceived audio frequencies, thepatient's implant fitting slope typically must be determined. Thisalternative implementation calculates or adjusts the implant fittingslope between each electrode instead of calculating a uniform slopeacross the entire electrode array as done in the implementationassociated with FIGS. 6 and 7, and may be described as follows. Thisalternative fitting routine provides a more accurateelectrode-to-frequency mapping on a per electrode basis but generallytakes more time to complete.

In general, this alternative implementation relies on the basic musictheory that given a note is comprised of a fundamental F1 having anamplitude A1 and a series of harmonics, e.g., a second harmonic F2, athird harmonic F3, and a nth harmonic Fn, where F2 is 2*F1, F3 is 3*F1,and Fn is n*F1, with each harmonic having a smaller amplitude A2 . . .n, e.g., where A2=0.1*A1, then a sound including the fundamental F1should sound the same to a normal hearing listener as a sound includingthe fundamental F1 and the small amplitude second harmonic F2. However,as mentioned above, due to the misalignment that typically results afteran electrode array is surgically inserted, a patient fitted with acochlear stimulation system typically will not reach the same conclusionas the normal hearing listener concerning the two same presentations.Nonetheless, a patient can still distinguish between sounds that areharmonically related and sounds that are not harmonically related. Thatis, if a patient is first presented with a sound including thefundamental F1 and then is next presented with a sound including thefundamental F1 and the small amplitude second harmonic F2, typically thepatient will determine that the two presentations do not sound the same,primarily because the delivered (actual) second harmonic is not what isperceived by the patient. But if the second harmonic F2 was adjusted bya frequency offset to take into account the electrode arraymisalignment, then the patient should perceive the presentation of thefundamental F1 to be the same as the presentation of the fundamental F1and the second harmonic adjusted by the offset, which may be referred toas the perceived second harmonic F2′.

This alternative implementation of the fitting routine may be describedin detail as follows.

The starting point is step 70. The next step is shown in box 71, wheretwo adjacent band pass filters, typically beginning with the second andthird lowest frequency filter (e.g., filter 2 and filter 3), areselected as a starting point for the tuning process. Alternatively anytwo filters may be chosen, i.e., the two filters do not necessarily needbe adjacent. For example, filter 1 and filter 3 may be selected and thefollowing steps may then be used to determine the implant fitting slopeof the electrodes associated with filter 1 and filter 3. Likewise,filter 3 and filter 8 may be selected and the following steps may thenbe used to determine the implant fitting slope of the electrodesassociated with filter 3 and filter 8.

The next step, as shown by box 72, is to select at random an initialposition of the small amplitude second harmonic F2 that is between thecenter frequencies of the two adjacent filters (or two arbitrarilychosen filters). Here, the second harmonic F2 was chosen to be 439 Hz.Next, as shown in box 73, the fundamental F1 of the second harmonicfrequency F2 is determined by using the formula F1=F2/2. In this case,the fundamental F1 is 219.5 Hz. The next step, indicated by box 74, isto select at random an estimate of the perceived second harmonicfrequency F2′ that is offset from F2 and between the center frequenciesof the two adjacent filters.

Next, as shown in box 75, the fundamental F1 is presented to the patientfor a short period of time, e.g., 0.5 to 1 second(s), so that thepatient has sufficient time to perceive the presented sound. Then, asshown in box 76, a sound including the fundamental F1 and the estimateof the perceived second harmonic F2′ is presented to the patient for asimilar period of time as the first sound presentation. Next, as shownin decision box 77, the patient compares the second sound presentation(i.e., F1 and F2′) to the first sound presentation (i.e., F1) anddetermines whether the two presentations sound different (or the same).If the patient determines the two sound presentations sound different,the patient may change his estimate of the perceived second harmonicfrequency F2′, as represented by the return arrow back to box 74 fromdecision box 77. That is, another estimate of the perceived secondharmonic frequency F2′ may be interactively chosen and the two soundpresentations once again can be played to the patient. In this iterativeprocess, the frequencies of the estimated perceived second harmonic F2′should begin to converge to a value wherein further increments becomesmaller and do not provide appreciable improvement to the perceivedsimilarity of the two presentations (F1 in one instance and F1 and F2′in another instance). The objective is to adjust the estimate of theperceived second harmonic F2′ until the two presentations sound the sameto the patient.

As shown in FIG. 8B, once no appreciable difference is detected betweenthe two presentations, the difference (Err) between the estimate of theperceived second harmonic F2′ and the actual second harmonic F2 isdetermined, as shown in box 78, by subtracting F2 from F2′, i.e.,Err=F2′−F2. Then, as shown in box 79, the center frequency of the higherfrequency filter (filter 2) is adjusted by the difference (Err) in thedirection of the estimate of the perceived second harmonic frequency F2′because it sounds to the patient like the actual second harmonic F2. Thealignment for that particular filter (e.g., filter 2) is now complete.The implant fitting slope between the electrodes associated with theselected filters may then be easily determined, where the slope ismm/octave.

The iterative fitting process for aligning the filters may be analogizedto the procedure for fitting eye glasses. The process for determininglens strength (diopters) is accomplished by presenting various lenseswith various lens strength in a manner to “zero in” on the optimal lensprescription. The method requires starting with a lens of a particularprescription. Another lens strength is picked and then the better of thetwo is picked. Armed with this knowledge, a third lens may be selectedand presented, and so forth, until a final, best lens is determined. Thesame iterative converging process may be used to determine the correctcenter frequency of the higher frequency filter of the two adjacentfilters.

Then, as shown in decision box 80, if there are additional filters toalign, the technique beginning at box 74 is applied to the filter justadjusted (e.g., filter 3) and the next higher frequency filter (e.g.,filter 4). If there are not any more filters to align, the technique iscompleted, as shown by box 81.

FIGS. 9A-9C illustrate in graphical form the alternative implementationof the fitting routine described in FIGS. 8A and 8B. As shown in FIG.9A, a small amplitude second harmonic F2 is selected between filter 1and filter 2. The fundamental F1 is shown to have a large amplitudecompared to the amplitude of the second harmonic F2. A random locationfor the harmonic F2′ is selected between filter 1 and filter 2. Here,the harmonic F2′ is estimated to have a higher frequency than the secondharmonic F2. Then, as shown in FIG. 9B, the patient is presented F1 fora short period of time (e.g., 1 to 2 seconds). After F1 is presented,then F1+F2′ is presented to the patient for the same amount of time. Ifthe two presentations sound different, the patient may change theestimate of the small amplitude harmonic F2′. If the two presentationssound the same, the difference between the harmonic F2′ and the secondharmonic F2 may be determined by the formula Err=F2′−F2. As shown inFIG. 9C, Err corresponds to the distance to move the center frequency ofthe higher frequency filter, i.e., filter 2, in the direction of F2′.This is because the harmonic F2′ would sound to the user like the secondharmonic F2. Once the filter 2 is adjusted, the same procedure may beused to adjust filter 3.

FIGS. 10A and 10B show an example of a user interface to a computersoftware program that can be used to implement the steps presented inFIGS. 8A and 8B. The user interface permits the patient to select asecond fundamental from a list of a range of frequencies (Hz) on the Yaxis 102. The X axis 104 represents the history for the fitting of aparticular filter (e.g., filter 2). Thus, the patent can see whichpositions he has already tried (as shown in FIG. 10A). Once the patientfinishes adjusting the second harmonic so that the two tones sound likea single note, the patient clicks on the right button of a mouse asdirected by the user interface (as shown at label 108). The filter(e.g., filter 2) is then adjusted by the amount of the error between thefrequency selected by the patient for the second harmonic and the actualposition of the second harmonic. As shown in FIG. 10B, the targetfrequency was 439 Hz, the estimate frequency was 419 Hz, and thecalculated implant line slope was 5.48 mm/octave. The patient may thenproceed to adjust the next filter.

The computational aspects described here can be implemented in analog ordigital electronic circuitry, or in computer hardware, firmware,software, or in combinations of them. Where appropriate, aspects ofthese systems and techniques can be implemented in a computer programproduct tangibly embodied in a machine-readable storage device forexecution by a programmable processor; and method steps can be performedby a programmable processor executing a program of instructions toperform functions by operating on input data and generating output.

A number of implementations have been described. Other implementationsmay include different or additional features, for example, the filtersassociated with the electrode contacts need not be adjusted uniformlyacross the entire electrode array. Rather, the filters may be adjusteddifferently based on the implant fitting slope between regions of theelectrode array. For example, in an electrode array having 16 electrodecontacts, the implant fitting slope can be determined between electrodes1-3 and the filters associated with electrodes 1-3 may be adjustedaccordingly. Likewise, the implant fitting slope between electrodes 4-6can be determined, and the filters associated with electrodes 4-6 may beadjusted accordingly, and so on in order to correctly map the electrodecontacts.

Accordingly, other implementations are within the scope of the followingclaims.

1. A method of fitting a user's cochlear implant system using acomputerized fitting system, wherein the cochlear implant systemincludes an electrode array having a plurality of electrodes implantedinto a cochlea of a user, the method comprising: presenting from thecomputerized fitting system a plurality of sounds to the user throughthe electrode array, wherein each sound comprises a plurality of notes;receiving from the user at the computerized fitting system a selectionof one of the plurality of sounds that most closely conforms to a singlenote; and determining at the computerized fitting system how to tune thecochlear implant system based on the received selection.
 2. The methodof claim 1, wherein presenting each of the sounds to the user throughthe electrode array is initiated by receiving from the user a uniquecomputerized fitting system input corresponding to one of the sounds. 3.The method of claim 2, wherein each unique computerized fitting systeminput comprises a unique key of the computerized fitting system, eachkey being associated with one of the sounds.
 4. The method of claim 1,wherein each electrode receives signals indicative of a band offrequencies in the plurality of sounds, and wherein determining how totune the cochlear implant system comprises adjusting the band offrequencies that at least one of the electrodes receives.
 5. The methodof claim 4, wherein adjusting the band of frequencies that at least oneelectrode receives comprises adjusting a center frequency of at leastone band pass filter in the cochlear implant system.
 6. The method ofclaim 1, wherein a lowest of the notes in each of the plurality ofsounds corresponds to a lowest center frequency of a band pass filter inthe cochlear implant system.
 7. The method of claim 1, wherein theimplanted electrode array is placed in the scale tympani and theplurality of electrodes are spaced along the electrode array.
 8. Themethod of claim 1, wherein determining how to tune the cochlear implantsystem comprises determining a slope of an implant fittingcharacteristic that defines a relationship between at least some of theelectrodes in the electrode array and one or more audio frequencies. 9.The method of claim 1, further comprising programming a speech processorof the cochlear implant system with the determined tuning.
 10. A methodof fitting a user's cochlear implant system using a computerized fittingsystem, wherein the cochlear implant system includes an electrode arrayhaving a plurality of electrodes implanted into a cochlea of a user, themethod comprising: presenting from the computerized fitting system afirst tone to the user through the electrode array, wherein the firsttone comprises a first frequency and a second frequency; presenting fromthe computerized fitting system a second tone to the user through theelectrode array, wherein the second tone comprises the first frequencybut not the second frequency; if the second tone does not sound like thefirst tone to the user, adjusting in the computerized fitting system thesecond frequency by an offset until the second tone sounds like thefirst tone to the user; and determining in the computerized fittingsystem how to tune the cochlear implant system using the offset.
 11. Themethod of claim 10, wherein the second frequency is a harmonic of thefirst frequency.
 12. The method of claim 10, wherein the adjusted secondfrequency is not a harmonic of the first frequency, but sounds like aharmonic of the first frequency to the user.
 13. The method of claim 10,wherein each electrode receives signals indicative of a band offrequencies, and wherein determining how to tune the cochlear implantsystem using the offset comprises adjusting the band of frequencies thatat least one of the electrodes receives.
 14. The method of claim 13,wherein adjusting the band of frequencies that at least one electrodereceives comprises adjusting a center frequency of at least one bandpass filter in the cochlear implant system.
 15. The method of claim 10,wherein the implanted electrode array is placed in the scale tympani andthe plurality of electrodes are spaced along the electrode array. 16.The method of claim 10, wherein the first and second tones are presentedat different times.
 17. The method of claim 16, wherein the first andsecond tones are presented for the same amount of time.
 18. The methodof claim 10, wherein determining how to tune the cochlear implant systemcomprises determining a slope of an implant fitting characteristic thatdefines a relationship between at least some of the electrodes in theelectrode array and audio frequencies.
 19. The method of claim 10,further comprising programming a speech processor of the cochlearimplant system with the determined tuning.
 20. A method of fitting auser's cochlear implant system using a computerized fitting system,wherein the cochlear implant system includes an electrode array having aplurality of electrodes implanted into a cochlea of a user, the methodcomprising: (a) presenting from the computerized fitting system a firsttone to the user through the electrode array, wherein the first tonecomprises a first frequency and a second frequency; (b) presenting fromthe computerized fitting system a second tone to the user through theelectrode array, wherein the second tone comprises the first frequencybut not the second frequency; (c) receiving from the user at thecomputerized fitting system an indication whether the second tone soundslike the first tone to the user; (d) if the first tone and the secondtone do not sound the same to the user, adjusting in the computerizedfitting system the second frequency by an offset and repeating steps (a)through (c); and (e) if the first tone and the second tone do sound thesame to the user, determining in the computerized fitting system how totune the cochlear implant system using the offset.
 21. The method ofclaim 20, wherein the second frequency is a harmonic of the firstfrequency.
 22. The method of claim 20, wherein the adjusted secondfrequency is not a harmonic of the first frequency, but sounds like aharmonic of the first frequency to the user.
 23. The method of claim 20,wherein each electrode receives signals indicative of a band offrequencies, and wherein determining how to tune the cochlear implantsystem using the offset comprises adjusting the band of frequencies thatat least one of the electrodes receives.
 24. The method of claim 23,wherein adjusting the band of frequencies that at least one electrodereceives comprises adjusting a center frequency of at least one bandpass filter in the cochlear implant system.
 25. The method of claim 20,wherein the first and second tones are presented at different times. 26.The method of claim 25, wherein the first and second tones are presentedfor the same amount of time.
 27. The method of claim 20, whereindetermining how to tune the cochlear implant system comprisesdetermining a slope of an implant fitting characteristic that defines arelationship between at least some of the electrodes in the electrodearray and audio frequencies.
 28. The method of claim 20, furthercomprising programming a speech processor of the cochlear implant systemwith the determined tuning.
 29. A method of fitting a user's cochlearimplant system using a computerized fitting system, wherein the cochlearimplant system includes an electrode array having a plurality ofelectrodes implanted into a cochlea of a user, wherein each electrodereceives signals within a frequency band, the method comprising:presenting from the computerized fitting system a first tone to the userthrough the electrode array comprising a first frequency and a secondfrequency, wherein the first frequency is within a first frequency bandand wherein the second frequency is within a second frequency band;adjusting in the computerized fitting system the second frequency in thefirst tone by a first offset until the first tone sounds like a singlenote to the user; and determining in the a computerized fitting systemhow to tune the second frequency band in the cochlear implant systemusing the first offset.
 30. The method of claim 29, wherein the adjustedsecond frequency sounds like a harmonic of the first frequency to theuser.
 31. The method of claim 30, wherein determining how to tune thesecond frequency band comprises determining how to tune a centerfrequency of the second frequency band.
 32. The method of claim 29,wherein the first and second frequency bands are adjacent.
 33. Themethod of claim 29, wherein the first frequency band is received at afirst electrode, and wherein the second frequency band is received at asecond electrode.
 34. The method of claim 29, further comprisingprogramming a band pass filter in a speech processor of the cochlearimplant system with the determined tuning for the second frequency band.35. The method of claim 29, subsequently comprising: presenting from thecomputerized fitting system a second tone to the user through theelectrode array comprising a third frequency and a fourth frequency,wherein the third frequency is within the second tuned frequency bandand wherein the fourth frequency is within a third frequency band;adjusting in the computerized fitting system the fourth frequency in thesecond tone by a second offset until the second tone sounds like asingle note; and determining in the computerized fitting system how totune the third frequency band in the cochlear implant system using thesecond offset.
 36. The method of claim 35, wherein the adjusted fourthfrequency sounds like a harmonic of the third frequency to the user. 37.The method of claim 36, wherein determining how to tune the thirdfrequency band comprises determining how to tune a center frequency ofthe third frequency band.
 38. The method of claim 35, wherein the secondand third frequency bands are adjacent.
 39. The method of claim 35,wherein the second tuned frequency band is received at a secondelectrode, and wherein the third frequency band is received at a thirdelectrode.
 40. The method of claim 35, further comprising programmingband pass filters in a speech processor of the cochlear implant systemwith the determined tunings for the second and third frequency bands.